From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH 2/2 net-next] tcp: sk_add_backlog() is too agressive
 for TCP
Date: Tue, 24 Apr 2012 10:56:43 +0200
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Cc: David Miller <davem@davemloft.net>, rick.jones2@hp.com,
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To: Ilpo =?ISO-8859-1?Q?J=E4rvinen?= <ilpo.jarvinen@helsinki.fi>
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On Tue, 2012-04-24 at 11:40 +0300, Ilpo J=C3=A4rvinen wrote:

> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 8bb6ade..33b87b2 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2820,7 +2820,11 @@ found:
>  	flush |=3D (__force int)(flags & TCP_FLAG_CWR);
>  	flush |=3D (__force int)((flags ^ tcp_flag_word(th2)) &
>  		  ~(TCP_FLAG_CWR | TCP_FLAG_FIN | TCP_FLAG_PSH));
> -	flush |=3D (__force int)(th->ack_seq ^ th2->ack_seq);
> +
> +	ackgap =3D skb_shinfo(p)->ack_size;
> +	ackdiff =3D th2->ack_seq - th->ack_seq;
> +	flush |=3D (ackdiff - 1) >=3D ackgap;
> +
>  	for (i =3D sizeof(*th); i < thlen; i +=3D 4)
>  		flush |=3D *(u32 *)((u8 *)th + i) ^
>  			 *(u32 *)((u8 *)th2 + i);
>=20

See how we duplicate tcp stack in GRO layer ;)

Really I have many doubts about GRO today.